Semiconductor fabrication processes are typically conducted with the substrates supported within a chamber under controlled conditions. For many purposes, semiconductor substrates (e.g., wafers) are heated inside the process chamber. For example, substrates can be heated by direct physical contact with an internally heated wafer holder or “chuck.” “Susceptors” are wafer supports used in systems where the wafer and susceptors absorb heat.
Some of the important controlled conditions for processing include, but are not limited to, pressure of the chamber, fluid flow rate into the chamber, temperature of the reaction chamber, temperature of the fluid flowing into the reaction chamber, and wafer position on the susceptor during wafer loading.
Heating within the reaction chamber can occur in a number of ways, including lamp banks or arrays positioned above the substrate surface for directly heating the susceptor or susceptor heaters/pedestal heaters positioned below the susceptor. Traditionally, the pedestal style heater extends into the chamber through a bottom wall and the susceptor is mounted on a top surface of the heater. The heater may include a resistive heating element enclosed within the heater to provide conductive heat and increase the susceptor temperature.
Consistent processing and consistent results generally require careful control and metering of processing gases in the system. One of the last resorts for controlling the processing gas is at the showerhead where the processing gas then contacts the wafer in the reaction chamber. Further, obtaining optimal flow rates and uniformity may be difficult at times due to showerhead holes becoming clogged or parasitic precursor reactions occurring within the showerhead.